Exercise apparatuses traditionally employed free weights to be lifted by the user or a weight stack actuated by a cable which is pulled by users of the apparatus. Recently, resistive elastic members, such as bands or plates, have been incorporated into exercise equipment to provide motion resistance. While these apparatuses provide beneficial resistive training, they are often relatively large and heavy, which prevents them from being easily transported and/or stored.
More recently, resistance exercise devices made nearly entirely of elastic bands have been gaining popularity. These elastic bands typically restrict the motion of a user's arms and/or legs, or the motion between the user and a support structure. Elastic exercise devices can be small, even portable, but have limited usefulness that results from their resistance characteristics, which depend on the length and elasticity of the elastic band. As a result of these characteristics, the elastic bands are useful for a specific length range, thus restricting the diversity of exercises for which it can be used. In addition, it may not be possible for different users to use the same device for the same exercise due to differences in height, weight, or strength between different users. Thus, for an elastic device to be generally useful, such as to provide a complete workout or to allow for different users, a plurality of elastic bands are required that must be easily interchangeable.
Another limitation of elastic resistance exercise devices is that the resistance is inconsistent and increases with increasing displacement, and also tends to snap back when the user decreases his or her effort. While this resistance response provides for a compact design, it is problematic as it does not recreate the resistance encountered by muscles during more natural types of exercising, such as running, swimming, etc. Yet another limitation of elastic devices is the inability to support a wide range of user weight. Rather, the devices are typically adapted to support only the resistance provided by the user's muscles. This further limits the exercises that can be performed by any individual elastic device. For this reason, elastic devices must be used over a limited range of stances, further limiting the user's workout.
Another type of resistance exercise device provides an inelastic strap that is attachable to a fixed location such as, for example, a door. These devices may overcome some of the limitations of the elastic devices previously discussed by providing inelastic straps that can be anchored between a door and a door jamb. Many traditional apparatuses incorporating inelastic straps have a fixed length and are limited in the range of exercises for which they can be used.
One type of resistance band apparatus is disclosed in U.S. Pat. No. 7,044,896 issued to Randal A. Hetrick and assigned to Fitness Anywhere, Inc. In this patent, an exercise device includes an inelastic adjustable length member with two arms and a grip at both ends. The inelastic adjustable length member is attached to a centrally located, flexible, strap based anchor that provides for a distribution of the length between the arms.